Clutch assembly

ABSTRACT

A clutch assembly for a roller door operator, the clutch assembly providing selective engagement with a drive wheel, the clutch assembly comprising: a rotatable shaft rotatable relative to the drive wheel; a clutch disc supported in a clutch lever and arranged to rotate with the rotatable shaft, the clutch disc and clutch lever configured to rotate relative to one another around the axis of rotation of the shaft; and a clutch cam supported in a clutch base, the clutch base configured to permit operative rotation of the clutch cam around the axis of rotation of the shaft in a first direction; wherein the clutch lever is operatively associated with the clutch cam so that rotational movement of the clutch lever in a second direction opposite to the first direction actuates movement of the clutch disc and the clutch lever axially along the rotatable shaft to engage or disengage the clutch disc with the drive wheel, and subsequent rotational movement of the clutch lever in the first direction actuates rotational movement of the clutch cam relative to the clutch base in the first direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Application Serial No.17/407346, filed Aug. 20, 2021 and entitled A CLUTCH ASSEMBLY which is acontinuation of U.S. Application Serial No. 16/576410, filed Sep. 19,2019 and entitled CLUTCH ASSEMBLY and also claims priority to Australianapplication number 2018903560, filed Sep. 21, 2018 and Australianapplication number 2018903651, filed Sep. 27, 2018, the entirety of eachof which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a clutch assembly. In particular, theclutch assembly is configured to engage and disengage an electric motorfrom a drive train. The present invention also provides a door operator(such as a roller door operator) including such a clutch assembly.

BACKGROUND OF THE INVENTION

Powered closures, such as sliding, roller, tilt or sectional doors,shutters, gates and the like are in common use for access control toareas, such as garages, car parks, private property, warehouses,factories, etc. Such closure arrangements are typically driven byoperator units incorporating electric motors coupled to drive theclosure between open and closed positions in an appropriate manner.

In the event of a power failure, fire or other unforeseen eventualities,the motor of such an operator unit may not be operable, and it istherefore desirable that manual operation of the closure be readilyachieved independently of the motor. Indeed, for safety reasons it isoften a requirement that selective manual operation be provided forpowered closures.

For roller doors or shutters in domestic applications where the operatorunit may be mounted above head height of a user, manual operation ofsuch closures may be achieved by way of disengaging a drive shaft from adrive train via a clutch assembly. Prior systems provide a clutch cordthat a user can pull to disengage the clutch assembly to allow formanual operation of the door. The user can pull the clutch cord again toreengage the clutch assembly to allow for motor driven door control.

In one form, such prior clutch assemblies use a leaf spring to act as aratchet pawl to provide this disengage and subsequent reengage action.However, the leaf springs are prone to wear and tear under normal useand can eventually break.

Further, when installing a door operator unit and setting the doortravel parameters, technicians can overestimate the downwards travel ofthe door. In this case, the bottom of the door hits the ground each timeit closes and this can cause a force to pass from the door, through thedrive train and ultimately to the leaf spring, causing the leaf springto buckle or fail.

Further, consumers and installation requirements now demand dooroperator units with slimmer profiles than in the past. Thus, for a givenpower of operator, it is desirable to provide a compact, low profileclutch assembly that can be accommodated with all related components ina generally slimmer profile door operator unit than hitherto available.

Reference to any prior art in the specification is not an acknowledgmentor suggestion that this prior art forms part of the common generalknowledge in any jurisdiction or that this prior art could reasonably beexpected to be understood, regarded as relevant, and/or combined withother pieces of prior art by a skilled person in the art.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a clutch assembly for aroller door operator, the clutch assembly providing selective engagementwith a drive wheel, the clutch assembly comprising: a rotatable shaftrotatable relative to the drive wheel; a clutch disc supported in aclutch lever and arranged to rotate with the rotatable shaft, the clutchdisc and clutch lever configured to rotate relative to one anotheraround the axis of rotation of the shaft; and a clutch cam supported ina clutch base, the clutch base configured to permit operative rotationof the clutch cam around the axis of rotation of the shaft in a firstdirection; wherein the clutch lever is operatively associated with theclutch cam so that rotational movement of the clutch lever in a seconddirection opposite to the first direction actuates movement of theclutch disc and the clutch lever axially along the rotatable shaft toengage or disengage the clutch disc with the drive wheel, and subsequentrotational movement of the clutch lever in the first direction actuatesrotational movement of the clutch cam relative to the clutch base in thefirst direction.

Advantageously, the present invention provides a clutch assembly for aroller door operator that eliminates the need for a leaf spring to actas a ratchet pawl in providing the disengage and engage action. Instead,the present invention utilises a clutch base and a clutch cam that aretogether configured to permit operative rotation of the clutch cam inonly one direction, whilst allowing the other components of the clutchassembly to move as is necessary as part of the engagement anddisengagement mechanism. To clarify, the permission of operativerotation in a single direction means that while rotation in the seconddirection may occur (to an extent), this rotation is prevented fromcontinuing to the point at which an operative action takes place. Thismeans the load that would ordinarily be borne by the leaf spring isinstead directed through the clutch base, which provides a more evendistribution of loading over a significantly larger load area (and thusthe bearing of greater loads) than possible with prior solutions.

Another advantage of the present invention is it affords a low profileclutch assembly, whereby a user can selectively engage or disengage themotor by a single pull on a clutch string or other actuating component.

In an embodiment, the clutch base comprises two or more base ramps andtwo or more base mating walls, and wherein the clutch cam comprises twoor more ratchet teeth, each of which comprises a rear surface and amating wall, wherein the rear surfaces of the ratchet teeth areconfigured to slide over the base ramps so causing abuttal of the basemating walls and the ratchet teeth to prevent rotational movement of theclutch cam relative to the clutch base in the second direction.

Advantageously, these surfaces of the clutch base and the clutch camtogether cooperate to permit rotation of the clutch cam in only a singledirection, as well as share the load ordinarily experienced by a leafspring in clutch assembly designs. In this embodiment, the base matingwalls are static, and thus do not experience the compression andflexures that a leaf spring experiences during each engagement anddisengagement action. Overall, the clutch assembly of this embodiment isless prone to the same level of wear. A further advantage arises in thatany overloading in this embodiment of the clutch assembly is sharedamongst a number of base mating walls as compared to a single leafspring experiencing the brunt of the load. The ratchet teeth maycomprise outriggers extending radially outwardly from the clutch cam.

In an embodiment, the clutch cam includes, extending around its frontsurface, a high flat adjacent a low flat with an engage mating wallprovided therebetween, wherein a clutch cam ramp extends between the lowflat to a peak higher than the high flat with a disengage mating wallprovided between the high flat and the peak. This configuration of theclutch cam provides a means of engagement for the clutch lever.

In an embodiment, the engagement of the clutch lever and the clutch camis realised by the clutch lever also comprising a rear surface includinga lever ramp and a lever mating wall, wherein the lever ramp slides overthe front surface of the clutch cam during rotational movement of theclutch lever in the second direction so causing abuttal of the levermating wall and one of the engage mating wall and the disengage matingwall, and wherein the clutch cam rotates in the first direction withsubsequent rotation of the clutch lever in the first direction. Thisparticular embodiment further enhances the desire to provide a low orflat profile clutch assembly by using specifically shaped surfaces thatprovide the necessary action for the clutch assembly to engage anddisengage with the motor, whilst still ensuring the clutch assembly issufficiently compact in order to fit within a conventional roller dooroperator.

In an embodiment, the clutch cam comprises an alignment tab protrudingover the engage mating wall. An advantage of the alignment tab is thatit allows for a slight back rotation of the clutch lever, which canassist with the engagement of the clutch disc and drive wheel.

In an embodiment, the clutch assembly includes a spring configured tostore torsional energy from the rotational movement of the clutch leverin the second direction, the spring also configured to release thestored torsional energy so causing the subsequent rotation of the clutchlever in the first direction. Preferably, the spring is a cylindricalspring. This further allows a compact profile of the clutch assembly.

In an embodiment, one end of the rotatable shaft provides input to aposition encoder. Advantageously, this provides a means to determine thelocation of the door directly from the rotatable shaft.

In another aspect, the present invention provides a clutch assembly fora door operator, providing selective engagement between a motor and adoor drive, the clutch assembly having a clutch base, a clutch cover anda clutch mechanism including one or more rotating cam or ratchetelements and configured to provide alternate engagement anddisengagement between the motor and door drive with successive actuationand release actions of a clutch lever between a first position and asecond position, the mechanism including a torsion spring to bias theclutch lever to said first position, wherein a part of the torsionspring can be accessed externally of the clutch cover in order topre-load the torsion spring once the clutch mechanism has been assembledbetween the clutch base and the clutch cover.

Preferably, the torsion spring also acts as a compression spring to biasthe components of the clutch mechanism together for operativeinteraction.

Preferably, the clutch cover includes a guidance part such as a slot(for example, an arcuate slot) through which said part of the torsionspring passes to afford external access thereto, the slot allowingmovement of said part of the torsion spring between positions ofincreasing torsional pre-load. The slot may include one or more detentpositions configured to provide retention of said part of the torsionspring in one or more prescribed pre-load states.

In an embodiment, the torsion spring is a substantially cylindricalspring. A first end portion of the torsion spring may be connected tothe clutch lever, said part of the torsion spring being the second endportion, arranged to protrude through the clutch cover. The second endportion may be shaped (eg. coiled) to provide for easy manualmanipulation in the pre-loading operation.

It will be understood that the torsion spring may include a separate orintegral handle which provides the accessibility of the torsion springexternal of the clutch cover.

Advantageously, this aspect of the invention allows that the componentsof the clutch assembly may be assembled before the torsion spring ispre-loaded (or before it is fully pre-loaded). This provides a saferassembly process for the clutch assembly, which otherwise would requirepre-loading (or higher pre-loading) of the torsion spring during theassembly process. Of further advantage is that a user can simply andconveniently provide the requisite pre-loading of the torsion springfrom a position external of the cover portion, without potentiallydisturbing the arrangement of the assembled components (as they aresecurely retained in their operational configuration between the clutchbase and the clutch cover) through the pre-loading operation.

In another aspect, the present invention provides a clutch assembly fora roller door operator, the clutch assembly providing selectiveengagement with a drive wheel, the clutch assembly comprising a clutchcam with a first and second face, having spaced ratchet elements on thefirst face to interact with spaced pawl elements on a supporting surfaceagainst which the cam rotates, the cam having spaced alternating axialoffset surfaces on the second face to interact with one or more spaceddrive elements on a clutch lever, such that successive actuations andreleases of the clutch lever alternately set different axial offsetsbetween the clutch lever and the supporting surface, so alternating arotatable driven element carried by the clutch lever between engaged anddisengaged conditions with a rotatable input drive element.

In yet another aspect, the present invention provides a clutch assemblyfor a roller door operator, the clutch assembly providing selectiveengagement between a motor and a door drive via a clutch assembly outputdrive shaft, the clutch assembly having a clutch base, a clutch coverand a clutch mechanism including one or more cam or ratchet elementsarranged to rotate around the axis of said clutch assembly output driveshaft and configured to provide alternate engagement and disengagementbetween the motor and the clutch assembly output drive shaft withsuccessive actuation and release actions of a clutch lever between afirst position and a second position, the clutch assembly including aposition encoder unit mountable to said clutch cover, the positionencoder unit having an input shaft arranged to be driven directly bysaid clutch assembly output drive shaft.

Preferably, said position encoder unit includes an absolute positionencoder, such as a Hall effect sensor arranged to sense the rotationalposition of a magnetic element driven by rotation of the positionencoder input shaft, configured such that 360° of rotation of themagnetic element corresponds to more than the full travel of a doordriven by the roller door operator. Preferably the position encoder unitincludes a worm gear drive connecting the position encoder input shaftand the magnetic element.

In this way, the clutch assembly and position encoder unit can beprovided as a single unit, which unit can also include a motor whenattached thereto. Providing all of these components in a single assemblysignificantly simplifies design and assembly of the door operator, atthe same time affording a very compact profile.

In a further aspect, the present invention provides a door operatorincluding a clutch assembly in accordance with any of the above-definedaspects.

As used herein, except where the context requires otherwise, the term“comprise” and variations of the term, such as “comprising”, “comprises”and “comprised”, are not intended to exclude further additives,components, integers or steps.

Further aspects of the present invention and further embodiments of theaspects described in the preceding paragraphs will become apparent fromthe following description, given by way of example and with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an installed garage roller door system;

FIG. 2 is a partial front elevation view of a garage door operator unit(with its casing removed) incorporating the clutch assembly of theinvention;

FIG. 3 is a plan view of an electric motor and gearbox used inconjunction with the clutch assembly of FIG. 2 ;

FIG. 4 a is a plan view of a clutch lever and a clutch disc, which arecomponents of the clutch assembly of FIG. 2 ;

FIG. 4 b is a side elevation cross section of the clutch lever andclutch disc of FIG. 4 a ;

FIG. 5 is a rear perspective view of the clutch disc of FIG. 4 a ;

FIG. 6 is a front perspective view of the electric motor and gearbox ofFIG. 3 with a clutch base, which is a component of the clutch assemblyof FIG. 2 ;

FIG. 7 is a front perspective view of the clutch base of FIG. 6 with aclutch cam, which is a component of the clutch assembly of FIG. 2 ;

FIG. 8 is a front perspective view of the clutch cam of FIG. 7 ;

FIG. 9 is a side elevation view of the clutch cam of FIG. 7 ;

FIG. 10 is a front perspective view of the clutch base of FIG. 6assembled with the clutch cam and the clutch lever and clutch disc ofFIG. 4 a , and a spring,

FIG. 11 is a rear perspective view of the clutch lever and clutch discof FIG. 4 a ;

FIG. 12 a is a rear perspective view of the clutch lever and clutch discof FIG. 4 a and the clutch cam of FIG. 7 showing part of the clutchassembly in an engaged state;

FIG. 12 b is a rear perspective view of the clutch lever and clutch discof FIG. 4 a and the clutch cam of FIG. 7 showing part of the clutchassembly in a disengaged state; and

FIG. 13 is a perspective view of the assembled clutch assembly of FIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates a roller door system 10 that includes a drum-mountedroller door 20 on an axle 30 mounted on end brackets 40 at each endthereof. At one end of axle 30, there is provided a door operator unit50. The door operator unit 50 includes a controller 60, which includesprogrammable circuitry to manage the various functions of the system.Controller 60 includes or is coupled to a signal receiver for receivingcontrol commands from a user’s remote control transmitter device (notshown). The roller door system 10 includes opposing guide tracks 80 a,bthat guide the travel of the door 20. Whilst FIG. 1 depicts a rollerdoor system, it will be understood that the invention herein describedis applicable to other forms of doors (eg. overhead doors, tilt doors,etc), gates, shutters, curtains and other types of movable closures.

Door opener unit 50 comprises a housing 52 that contains variousmechanical and electrical componentry used to operate the unit, i.e.drive movement of the roller door 20 between open and closed positionsby moving the roller door 20 along the guide tracks 80 a,b. The dooroperator unit 50 includes an electric motor 210 and an associated drivetrain (FIG. 2 ). Door operator unit 50 also includes pull handle 70 forengaging and disengaging the drive train from roller door 20 in theevent manual operation of the door is required. For example, a power cutor failure of one or more of the mechanical and electrically componentrymay necessitate a user to manually open or close the door 20.

Reference is now made to FIG. 2 , which illustrates a portion of thefront of the door opener unit 50 with a cover of the housing 52 removed.Any reference to the “front” of the operator unit 50 or the componentstherein is a reference to the view shown in FIG. 2 . References to“clockwise” or “counter clockwise” are to be taken about the perspectiveshown in FIG. 2 . Reference to “downward” is taken to be towards thelower end of FIG. 2 .

The door operator unit 50 comprises a clutch assembly 1300 of anembodiment the present invention that will be described in greaterdetail below. The door operator unit also includes a transformer 200arranged to be electrically connected to AC mains power via a power lead202 that plugs into a wall socket. The transformer steps down thereceived mains power for ultimate transmission to the electric motor 210at a suitable voltage level via, for example, a rectifier provided on aprinted circuit board 212. The transformer 200 is held in place in partby a transformer washer 204. In an embodiment, the electric motor is a24V DC electric motor, though any suitable motor may be used. Theelectric motor 210 drives a drive train that ultimately opens or closesthe door 20 when the clutch assembly 1300 is engaged.

Engagement and disengagement of the clutch assembly 1300 is achieved bythe application of a pulling force on a clutch pull cord 208, which isthreaded through a clutch assembly lever 402. This engagement will bedescribed in greater detail below. The clutch pull rod 208 follows apre-determined path within the housing 52, where it is guided andmaintained along this path by a pull cord guide 54, mounted withinhousing 52 and adjacent transformer 202. The pull cord guide 54alleviates the need for any additional anchoring point within thehousing 52, which typically has limited spacing amongst the tightlypacked electrical and mechanical components. From the clutch assemblylever 402, the clutch pull cord 208 extends downward along the path,through pull cord guide 54 and ultimately extends downward and away fromthe door operator unit 50 near the centre of housing 52 for remoteactuation of the clutch assembly 1300 by a user. It will be understoodthat when the user applies a pulling force on pull handle 70 (i.e.provides a pulling force on clutch pull cord 208), the clutch assemblylever 402 will move in the downward direction, rotating clockwise,leading to engagement or disengagement of clutch assembly 1300.

Reference is now made to FIG. 3 , which shows a gearbox base 300 used inconjunction with the clutch assembly 1300 of this embodiment. Electricmotor 210 drives the drive train, which includes the gearing arrangementcontained within gearbox housing 308, that ultimately causes the door 20to open or close when the clutch assembly 1300 is engaged. Gearbox base300 is positioned within operator unit 50, with gearbox housing 308secured inside the housing 52 of operator unit 50 and also to electricmotor 210, thereby securing the electric motor 210 inside the dooroperator unit 50. The electric motor 210 is attached to the gearbox base300 by a motor base 303. Motor base 303 may be integral with gearboxbase 300, or a separate component secured between the gearbox base 300and the electric motor 210.

Electric motor 210 comprises an output shaft 302 that is connected to orcomprises a worm gear 304. When the worm gear 304 is driven by theoutput shaft 302, the worm gear 304 in turn drives a drive wheel 306.The drive wheel 306 is mounted for rotation within gearbox housing 308.The drive wheel 306 is typically a helical gear, although other suitablegear types may be used. Drive wheel 306 includes a planar front surface307, a planar rear surface parallel and longitudinally spaced from theplanar front surface 307, and a side surface having a plurality ofhelical gear teeth 310.

Drive wheel 306 is driven by worm gear 304 by the meshing of worm gear304 with the teeth 310 of the drive wheel 306. A rotatable shaft 312passes through a central aperture of the drive wheel 306 and protrudesin a perpendicular direction to the front surface 307 of drive wheel306. When clutch assembly 1300 is disengaged, the rotatable shaft 312 isfreely rotatable relative to drive wheel 306. This allows for manualoperation of the door 20. This is because rotation of the rotatableshaft 312 causes rotation of a pinion 602 (FIG. 6 ) positioned on theopposite end of the rotatable shaft (the pinion 602 and rotatable shaft312 are fixedly connected or integral with each other), which drives adrum (such as an internally geared drum) provided on door operator unit50 and connected to a roller drum of the door 20, thereby causing door20 to move between open and closed positions.

Referring to FIGS. 3, 4 a and 4 b , rotatable shaft 312 is configured tobe received by a clutch disc 400 that comprises part of clutch assembly1300. Rotatable shaft 312 is in rotatable engagement with clutch disc400 such that the two rotate together irrespective of whether clutchassembly 1300 is engaged or disengaged. When the clutch assembly 1300 isengaged, closing and opening of door 20 is controlled by the output ofelectric motor 210, i.e. the output shaft 302 causes rotation of worm304, which in turn rotates drive wheel 306, which in turn drives clutchdisc 400 and thus rotatable shaft 312. When the clutch assembly 1300 isdisengaged, manual operation of door 20 is allowed. Manual movement ofthe door 20 causes pinion 602 and thus rotatable shaft 312 to rotate(which is free to rotate within drive wheel 306), which in turn drivesclutch disc 400, which is free to rotate within clutch lever 402.

Clutch disc 400 is mounted for rotation on clutch lever 402 (whichitself forms part of clutch assembly 1300). Clutch disc 400 is freelyrotatable relative to clutch lever 402, i.e. clutch disc 400 and clutchlever 402 rotate relative to each other about the longitudinal axis ofrotatable shaft 312. In this embodiment, clutch disc 400 is held inrotatable engagement with clutch lever 402 by a thrust washer 404 and acirclip 406. Circlip 406 engages a groove 408 in clutch disc 400.

Clutch disc 400 and clutch lever 402 are thus configured to movetogether in the axial direction of rotatable shaft 312. As described infurther detail below, when the clutch assembly 1300 moves from anengaged position to a disengaged position, the clutch disc 400 alongwith clutch lever assembly 402 move in the axial direction alongrotatable shaft 312 away from drive wheel 306. Conversely, when theclutch assembly 1300 moves from a disengaged position to an engagedposition, the clutch disc 400 along with clutch lever assembly 402 movein the axial direction along rotatable shaft 312 towards drive wheel306. Clutch disc 400 is keyed to rotatable shaft 312 in any suitablemanner. In the depicted embodiment, the rotatable shaft 312 has ahexagonal cross-section that is configured to be received by acommensurate hexagonal aperture 410 provided in clutch disc 400.However, the rotatable shaft 312 and aperture 410 may assume othercommensurate shapes. For example, a spline joint between the rotatableshaft 312 and aperture 410 may be used.

The clutch assembly 1300 is configured to be selectively engageable withdrive wheel 306. Specifically, clutch disc 400 is configured to engagewith drive wheel 306 by being pushed axially along rotatable shaft 312towards the drive wheel’s front surface 307, and clutch disc 400 isconfigured to disengage with drive wheel 306 by being pushed axiallyalong rotatable shaft 312 in the other direction away from the drivewheel’s front surface 307.

Drive wheel 306 is not able to move axially within gearbox housing 308,i.e. its movement is limited to rotation about the longitudinal axis ofthe rotatable shaft 312. A circlip 314 is provided on the front surface307 of drive wheel 306 in a groove around rotatable shaft 312 in orderto prevent axial movement of drive wheel 306 along the rotatable shaft312.

As will be understood, the auto-locking nature of worm drives ensuresthat drive wheel 306 cannot be driven manually. That is, movement ofdrive wheel 306 can only be driven by worm 304 when worm 304 is drivenby electric motor 210, be it clockwise or anticlockwise depending onwhich way output shaft 302 and thus worm 304 is driven by the electricmotor 210. Consequently, whether door 20 is being opened or closed isdependent on whether the electric motor is driven forwards or backwards.

Engagement of drive wheel 306 and clutch disc 400 can be achieved in anysuitable manner. In this embodiment, drive wheel 306 includes aplurality of recesses 316 angularly equispaced about rotatable shaft 312in front surface 307. Recesses 316 are configured to receive a pluralityof dogs 500 that extend from a rear surface 502 of clutch disc 400 (FIG.5 ). The dogs 500 are similarly angularly equispaced about aperture 410on the rear surface 502 of clutch disc 400. Axial movement of the clutchdisc 400 along the rotatable shaft 312 towards the drive wheel 306causes the dogs 500 to be received within recesses 316. Conversely,axial movement of the clutch disc 400 away from the drive wheel 306causes the dogs 500 to move out of engagement with the recesses 316 ofdrive wheel 306. Engagement of the dogs 500 in recesses 316 thereforekeys the clutch disc 400 to the drive wheel 306 so that the two rotatetogether. The number of dogs 500 may be less than the number ofrecesses, or there may be the same number of dogs as recesses. As itwill be appreciated by a person skilled in the art, the positioning ofthe dogs and recesses may be mutually interchangeable, i.e. the dogs 500may instead be on the drive wheel 306 with the recesses on clutch disc400.

In view of the description above, it will be clear to a person skilledin the art that when clutch disc 400 is moved axially along rotatableshaft 312 towards the front surface 307 of drive wheel 306 and engageswith drive wheel 306, manual rotation of rotatable shaft 312 isprevented. This is because of the combination of: drive wheel 306 notbeing rotatable manually due to the nature of worm drive systemspreventing back driving of the motor; clutch disc 400 being engaged andthus locked to drive wheel 306; the rotatable engagement between clutchdisc 400 and rotatable shaft 312; clutch disc 400 being prevented fromrotating means that rotatable shaft 312 is prevented from rotating.Thus, when the clutch assembly 1300 is engaged, door 20 can only beopened or closed when the electric motor 210 causes worm 304 to drivethe drive wheel 306. It logically follows that when clutch disc 400 ismoved axially along rotatable shaft 312 away from the front surface 307of drive wheel 306 and disengages with drive wheel 306, rotatable shaft312 can be manually rotated. This is because clutch disc 400 is free torotate within clutch lever 402. A user manually moving the door open orclosed causes the door drum to rotate, thus causing the pinion 602 torotate which causes the rotatable shaft 312 and clutch disc 400 torotate.

Further components of the clutch assembly 1300 will now be described.With reference to FIG. 6 , there is provided a clutch base 600 fixedlymounted on gearbox base 300. Clutch base 600 may be mounted to gearboxbase 300 in any suitable manner so that there is no relative movementbetween the clutch base 600 and gearbox base 300. In this embodiment,clutch base 600 includes fastening surfaces 604. Fastening surfaces 604are intended to rest on corresponding surfaces of gearbox base 300 andreceive screws through a number of holes to fixedly connect the clutchbase 600 with gearbox base 300. Clutch base 600 includes a through-bore606 through which rotatable shaft 312 passes when clutch base 600 ismounted on gearbox base 300. Through-bore 606 allows front surface 307of drive wheel 306 to be exposed and allows for clutch disc 400 to bemoved forward and back through through-bore 606 for engagement anddisengagement of clutch assembly 1300.

Clutch base 600 includes an internally directed continuous flange 608extending from a rear surface of clutch base 600, flange 608 beingperipheral to through-bore 606. The front surface of flange 608 supportsa plurality of base ramps 610 that extend from adjacent base flats 612.Between respective base ramps 610 and base flats 612 is a base matingwall 613. The base mating walls 613 are angularly equispaced around theperiphery of through-bore 606. In the depicted embodiment, there arefour base ramps 610, four base flats 612 and four base mating walls 613,all with mutual 90° separation, although any suitable number of thesecomponents may be provided (typically an equal number of each componentwill be provided). In an alternative embodiment, the gearbox base 300may support the base ramps 610, base flats 612 and base mating walls613, without the need for a separate clutch base 600. In such a case,gearbox base 300 comprises part of the clutch assembly 1300.

Travelling circumferentially around flange 608 (and from the perspectivedepicted in FIG. 6 ), each base ramp 610 initiates at the level of anadjacent base flat 612 and, following the curvature of arcuate flange608, rises to a peak, at which a peak flat 614 is provided. The baseramp 610 then abruptly falls to meet the beginning of the next base flat612, thereby defining the base mating wall 613. Thus, four base matingwalls are provided equispaced 90° around flange 608. The base flats 612are all on the same level, i.e. on a plane perpendicular to thethrough-bore 606. The peak flats 614 are also on a common level, i.e. ona plane perpendicular to a longitudinal axis of the through-bore 606 andspaced axially away from the plane of the base flats 612, which isparallel to the plane of the peak flats 614, by the distance or lengthof the base mating wall 613 i.e. the distance between the base flat andpeak flat. In an embodiment, the arcs of base flats 612 are longer thanthe arcs of base ramps 610 when viewed from above.

Each base mating wall 613 acts as a ratchet pawl in that it isconfigured to permit rotation of a clutch cam 700 (FIGS. 7 and 8 )around the longitudinal axis of rotatable shaft 312 in one operativedirection (counter clockwise in the depicted embodiments). By operativedirection, what is meant is that rotation in the opposite direction willbe stopped and thus have no operative effect (as described below). Thisconstruction is particularly advantageous over prior clutch assembliesthat utilised leaf springs in place of the present mating walls 613.Leaf springs are prone to failure from wear and overloading, an issuethat at least this embodiment of the present invention generally avoids,as the base mating walls 613 are static, and thus do not experience thecompression and flexures that a leaf spring experiences during eachengagement and disengagement action. Overall, the present constructionis less prone to the same level of wear. A further advantage arises inthat forces in the present clutch assembly 1300 are shared amongst anumber of base mating walls 613 as compared to a single leaf springexperiencing the totality of the load.

As will become apparent with regard to this embodiment, the engagementand disengagement of clutch assembly 1300 (through the axial movement ofclutch disc 400 in and out of engagement with drive wheel 306) isprovided by rotational movement of various components by at least 90°,i.e. the angle between successive base mating walls 613. In analternative variant including only two base ramps 610, two base flats612 and two base mating walls 613, rotation of various components by atleast 180° causes the engagement and disengagement of clutch assembly1300.

With reference to FIG. 7 , clutch cam 700 can be shown when in positionand supported by clutch base 600. In the depicted embodiment, clutch cam700 is supported on flange 608 of clutch base 600. Clutch cam 700includes a ring-shaped front surface 701. Clutch cam 700 includes athrough-bore 702 through which rotatable shaft 312 and clutch disc 400pass, similarly to clutch base 600. Specific features of clutch cam 700are shown in FIGS. 8 and 9 . Clutch cam 700 includes one or moreoutriggers 810, each of which comprises a rear outrigger surface 818, anoutrigger mating wall 814, and an outrigger ramp section 900 adjacentthe rear outrigger surface 818. The outrigger mating walls 814 aretypically spaced equidistant around the clutch cam 700. The one or moreoutriggers 810 project raidally outwardly from clutch cam 700. In thedepicted embodiment, four outriggers 810 project out from an externalperiphery or side wall of clutch cam 700.

Each outrigger has a first end surface that lines up with, is in thesame plane as and is an extension of a corresponding mating wall 806,808. This first end surface defines outrigger mating wall 814. Outriggerramp section 900 slopes upwards (relative to the view in FIG. 9 ) fromrear outrigger surface 818 towards an outrigger front surface 819 andtowards a second end surface (opposed the first end surface) of theoutrigger 810. The slope corresponds to and follows the same arcuatepath as the slope of base ramps 610.

The rear outrigger surfaces 818 are configured to slide over theabutting surfaces on the clutch base 600, thereby allowing rotation ofclutch cam 700 relative to clutch base 600. This rotation in a counterclockwise direction is caused by a force applied by clutch lever 402,which sits on top (relative to the view shown in FIG. 10 ) of clutch cam700 as will be described below. For example, the rear outrigger surfaces818 are moved over flange 608 of clutch base 600. When the rearoutrigger surface 818 moves from a base flat 612 along and over baseramps 610, the outrigger 810 slips, i.e. moves axially towards the frontsurface 307 of drive wheel 306, wherein the base mating walls 613 andthe outrigger mating walls 814 abut. The abuttal prevents rotationalmovement in an opposite direction (clockwise in the depicted embodiment)of the clutch cam 700 relative to the clutch base 600. Preferably, thesame number of outriggers 810 (and thus outrigger mating walls 814) ispresent as base ramps 610, base flats 612 and base mating walls 613.When clutch cam 700 is positioned in clutch base 600, the rear surface818 of each outrigger 810 sits on the front surface (i.e. the surfacecomprising base ramps 610 and base flats 612) of flange 608; andexternal side surface 812 of clutch cam 700 sits adjacent the internalside surface of flange 608.

Travelling circumferentially around front surface 701 of clutch cam 700,there is provided a high flat 804 adjacent to a low flat 802 with anengage mating wall 808, defined by a drop off wall, providedtherebetween. It will be appreciated from the description and certainfigures, that references to “high” in this context will mean being morefrontward and references to “low” in this context will mean being morerearward. The high flat 804 and low flat 802 are flat surfaces of frontsurface 701 of the clutch cam 700, with the high flat assuming a higherposition relative to low flat 808. The high flat 804 extends 90° aroundthe front surface 701 before falling to meet the beginning of theadjacent low flat 802. From the low flat 802, a clutch cam ramp 800begins and culminates at a clutch cam peak surface 801. Clutch cam peaksurface 801 is higher, i.e. more frontward, than high flat 804. The arcfrom the beginning of a low flat 802 to the end of clutch cam peaksurface 801 of clutch cam ramp 800 is 90°. A disengage mating wall 806,defined by another drop off wall, is provided between the clutch campeak surface 801 and an adjacent high flat 804. It will be appreciatedthat the height of engage mating wall 808 (the drop between a high flat804 and low flat 802) is greater than the height of a disengage matingwall 806 (the drop between clutch cam peak surface 801 and high flat804).

In this way, progressing clockwise around clutch cam 700, as depicted inFIG. 8 , from point A (0°), the clutch cam’s front surface 701 followsthis sequence: low flat 802, clutch ramp 800, clutch cam peak surface801, disengage mating wall 806 (90°), high flat 804, engage mating wall808 (180°), low flat 802, clutch ramp 800, disengage mating wall 806(270°), high flat 804, engage mating wall 808 (360°). In the depictedembodiment, there are two each of high flats 804, low flats 802, clutchcam ramps 800, disengage mating walls 806 and engage mating walls 808.However, any suitable number of these components may be provided.Similarly to the clutch base 600, clutch cam 700 has a mating wall (beit an engage mating wall 808 or disengage mating wall 806) providedangularly spaced equidistant around clutch cam 700. The four matingwalls 806, 808 provide an engagement or disengagement action by therelative rotational movement of various components by 90°. As would beclear from the figures, engagement and disengagement of the clutchassembly 1300 will thus be effected by rotation of the clutch cam 700 byat least 90° within clutch base 600.

In the depicted embodiment, clutch cam 700 includes one or morealignment tabs 816 protruding outwardly from high flat 804 and engagemating wall 808 and over low flat 802. When the clutch assembly 1300 isengaged, alignment tabs 816 allow for a slight over-rotation of clutchlever 402. When the rear surfaces of clutch lever 402 (described indetail below) pass over alignment tabs 816, it will be forced axiallyrearward (i.e. towards drive wheel 306) along rotatable shaft 312(causing engagement of the clutch assembly) and then slightly rotateback to abut with engage mating wall 808. This slight back rotationassists with clutch disc 400 and drive wheel 306 engaging, for example,by aiding the alignment of the corresponding recesses 316 and dogs 500.

When clutch cam 700 rotates, ramp sections 900 engage with base ramps610, and the outrigger rear surface 818 slide across base ramps 610,causing clutch cam 700 to rise (i.e. axially along the length ofrotatable shaft 312 away from drive wheel 306) relative to clutch base600. The outrigger mating walls 814 move slightly beyond theircorresponding base mating walls and the outrigger rear surfaces 818 droponto base flats 612. During this rotation, clutch cam 700 rotates 90°.Clutch cam 700 can only operatively rotate counter clockwise in theembodiment illustrated in the drawings. This is because once clutch cam700 drops, clockwise rotation of clutch cam 700 will be stopped whenbase mating walls 613 engage and abut with outrigger mating walls 814.This 90° clutch cam 700 rotation is repeated each time the lever ispulled. Hence, a ratchet mechanism is provided between clutch base 600and clutch cam 700, with ratchet teeth provided by outrigger matingwalls 814 (spaced every 90°), and pawls provided by base mating walls613 (spaced every 90°).

Reference is now made to FIGS. 10 and 11 , which illustrate thefunctioning of clutch lever 402. Clutch lever 402 is supported in clutchbase 600, with clutch base 600 configured to allow rotation of clutchlever 402 therein. A spring 1000 is supported in clutch lever 402 andabove (from the perspective of FIG. 10 ) clutch disc 400. A first end(obscured) of spring 1000 is fixed to clutch lever 402 and thus rotateswith clutch lever 402. A second end 1000 a of spring 1000 is fixed to acomponent that does not rotate with clutch lever 402, namely clutch cap1302 (FIG. 13 ). Spring 1000 has two functions in the clutch assembly1300. First, spring 1000 provides an axial compression force downwards,i.e. towards drive wheel 306, to clutch lever 402 and clutch disc 400 inorder to engage clutch disc 400 with drive wheel 306. Secondly, spring1000 provides a torsional return force to clutch lever 402. In thisembodiment, spring 1000 is a cylindrical spring. This allows the clutchassembly 1300 to have an overall thinner profile. However, other springsmay be used that allow for suitable functioning of the clutch assembly1300.

With reference to FIG. 10 , a user pulls a lever arm 1002 (via pullhandle 70 and clutch pull cord 208) connected to or integral with clutchlever 402, thereby causing clutch lever 402 to rotate clockwise from aninitial resting position to an actuated position (when lever arm 1002 isrotated from the rest position to position B). Lever arm 1002 comprisesan aperture 1004 configured to receive clutch pull cord 208 (not shownin FIG. 10 ). The clutch string 208 may be tied or looped so that a usercan actuate clutch lever 402 remotely. The pulling of the lever arm 1002applies a torsional force on spring 1000, thereby storing energy in thespring 1000. When the clutch lever 402 is actuated, i.e. causingengagement or disengagement of the clutch assembly 1300, the userreleases the force on the lever arm 1002. The stored energy in thespring 1000 will be released, and thereby rotates clutch lever 402anticlockwise back to the rest position.

FIG. 11 shows the rear side of clutch lever 402 and the surfaces thatcooperate with the front surface 701 of clutch cam 700 when clutch lever402 is actuated. There is provided on the rear side of clutch lever 402two arcuate lever ramps 1100 adjacent to two arcuate lever flats 1102.Each lever ramp 1100 initiates from a lever flat 1102, and following thecurvature thereof rises to a peak height (similarly to previouslydescribed ramps and peaks). Adjacent the peak of the ramp is a leverramp flat 1106, i.e. a flat surface at the peak height of the ramp.Lever ramp 1100 then abruptly falls from the lever ramp flat 1106 tomeet the beginning of the next lever flat 1102, thereby defining a levermating wall 1104. In this embodiment, two lever mating walls 1104 areprovided 180° apart around the rear side of clutch lever 402. However,any suitable number of lever ramps may be provided in accordance withthe particular detail of the clutch design.

Referring to FIGS. 8, 11, 12 a and 12 b and as mentioned above, whenclutch assembly 1300 is assembled, clutch base 600 supports clutch cam700 and clutch lever 402. FIG. 12 a shows clutch disc 400 in an engagedposition (i.e. dogs 500 are engaged with recesses 316 on drive wheel306). In this engaged position, lever mating wall 1104 is in closeproximity to or abuts clutch cam’s engage mating wall 808, and leverramp flat 1106 is disposed against clutch cam’s low flat 802. In thisembodiment, an identical configuration is provided on the obscuredopposite side. Clutch lever 402 and thus clutch disc 400 are in alowered (more rearward) position because lever ramps 1100 abut low flats802 rather than high flats 804. This also means that clutch disc 400 anddogs 500 protrude out of clutch cam 700 (and would also protrude throughthe clutch base’s through-bore 606). Clutch disc 400 can now bedisengaged (i.e. moved along with cam lever 402 axially away from drivewheel 306) by a user rotating cam lever 402 clockwise. This causes leverramp flat 1106 to slide along low flat 802 and onto and along clutch camramp 800. Lever ramp 1100 slides along clutch cam ramp 800, rising untillever ramp flat 1106 drops off disengage mating wall 806 and onto highflat 804 of clutch cam 700. This brings lever ramp flat 1106 intocontact with high flat 804 and lever mating wall 1104 into abuttal withdisengage mating wall 806.

During this time, both torsional energy (i.e. twisting) and axial energy(i.e. compressing) is provided to and stored in spring 1000. Also duringthis time, the friction force created by movement of lever ramp 1100along clutch cam low flat 802 and ramp 800 urges clutch cam 700 to alsorotate in the clockwise direction. However, this clockwise rotation ofclutch cam 700 is prevented or stopped when there is engagement ofoutrigger mating walls 814 with opposing clutch base mating walls 613.When the user releases the load on lever arm 1002, spring 1000 releasesits stored torsional energy causing clutch lever 402 to rotate 90°counter clockwise back to its rest position. Clutch cam 700 also rotates90° counter clockwise in clutch base 600 due to the engagement of levermating wall 1104 with disengage mating wall 806. The outrigger bottomsurfaces 818 slide along and over clutch base ramps 610 during thisrotation of clutch cam 700. As shown in FIG. 12 b , clutch disc 400 isnow disengaged from drive wheel 306. This means that rotatable shaft 312is free to rotate (eg. by manual operation of the door, as explainedabove). Rotation of rotatable shaft 312 will cause clutch disc 400 torotate within clutch lever 402 (clutch lever 402 will remain stationaryin its rest position).

In the current disengaged state, lever mating wall 1104 is abutting orin close proximity to disengage mating wall 806 of clutch cam 700, andlever ramp flat 1106 is disposed against high flat 804 of clutch cam700. The same configuration is provided on the opposite (obscured) side.Clutch lever 402 is in a raised (more forward) position because leverramps 1100 abut high flats 804 rather than low flats 802 as would be thecase in the engaged position. It will be clear that in the currentposition dogs 500 of clutch disc 400 are above the beginning ofthrough-bore 702 of clutch cam 700, i.e. away from the front surface 307of drive wheel 306.

In order to reengage the clutch assembly 1300, a similar process takesplace, whereby a user rotates cam lever 402 clockwise approximately 90°by applying a suitable force on lever arm 1002. This rotation causeslever ramp flat 1106 to slide along the full arc of high flat 804 untillever ramp flat 1106 drops off engage mating wall 808. This drop isassisted (or indeed forced) by spring 1000 releasing its stored axialenergy. The drop brings lever ramp flat 1106 into contact with low flat802 and lever mating wall 1104 into contact with engage mating wall 808.Torsional energy is stored in spring 1000 by the user’s clockwiserotation of cam lever 402. During this rotation, the friction forcecreated by movement of lever ramp flat 1106 along high flat 804 urgesclutch cam 700 to also rotate in the clockwise direction. However, thisclockwise rotation of clutch cam 700 is again prevented by theengagement of outrigger mating walls 814 with opposing clutch basemating walls 613. When the user releases lever arm 1002, spring 1000releases its stored torsional energy causing clutch lever 402 to rotate90° counter clockwise back to its rest position. Clutch cam 700 alsorotates 90° counter clockwise in clutch base 600 due to the engagementof lever mating wall 1104 with engage mating wall 808. The outriggerrear surfaces 818 slide along and over clutch base ramps 610 during thisrotation of clutch cam 700. This returns the mechanism to theconfiguration shown in FIG. 12 with the clutch disc 400 engaged withdrive wheel 306. This means that rotatable shaft 312 cannot be movedmanually, but instead only by the drive from electric motor 210. Again,rotation of clutch disc 400 within clutch lever 402 (clutch lever 402will remain stationary in its rest position) will cause rotatable shaft312 to rotate.

FIG. 13 illustrates the clutch assembly 1300 in an assembled state. Theclutch assembly includes clutch base 600, clutch cam 700, clutch disc400, clutch lever 402, and clutch cap 1302. The second end 1000 a ofspring 1000 is held to the clutch cap 1302 through an arcuate slot 1308.A benefit that arises from this clutch assembly configuration is theability of a user to torsionally and selectively pre-load the spring1000 after the clutch assembly 1300 is in the assembled state andinstalled for use. The second end 1000 a of spring 1000 protrudes fromclutch cap 1302 and is of a shape or configuration (eg. coiled, asshown) that provides convenient engagement for the user, who canmanually move, such as by finger action or tool manipulation, the secondend 1000 a of the spring 1000 from one end of the arcuate slot 1308 toone of two retention side slots 1309, 1309′, shaped to provide detentpositions for the second end 1000 a of the spring 1000.

FIG. 13 shows the second end 1000 a of the spring 1000 in its initialposition (light pre-load). First side slot 1309 provides a firstalternative pre-load position, whilst second side slot 1309′ provides asecond alternative (higher spring torsion) pre-load position. Once movedto the one of the side slots 1309, 1309′, the second end 1000 a of thespring 1000 is held in that position, thereby storing correspondingtorsional energy in the spring 1000. The ability to selectivelytorsionally pre-load the spring 1000 after the clutch assembly 1300 hasbeen assembled improves, amongst other things, the safety and ease ofassembly of the clutch assembly 1300. It will be appreciated that thenumber of side slots can vary as desired, to provide multiple differenttorsion spring pre-load options.

Clutch cap 1302 is mounted to clutch base 600 via screws passed throughcorresponding fastening flanges 1304. Clutch cap 1302 provides suitablelimits to the movement of clutch lever 402. In particular, a partialclutch cap side wall 1306 provides a void that allows lever arm 1002(and thus clutch lever 402) to move between (at least) its restingposition (as illustrated) and clutch actuation point B. The clutch capside wall 1306 also prevents the lever arm 1002 from further movement byacting as a stop to further rotation of lever arm 1002.

Clutch cap 1302 also provides a shaping (eg. a shaped recessed portion)for location of a position encoder assembly 1320 (see FIGS. 2, 13 ),position encoder assembly 1320 comprising the mechanical and electricalcomponents to determine the angular position of shaft 312, and thereforethe angular position of the door driven therefrom. For this purpose,position encoder assembly 1320 includes an encoder input shaft thatengages with a slot provided at the end of rotatable shaft 312 (see FIG.6 ). The encoder input shaft includes a worm arranged to drive a gearwhich carries or is connected to a magnet, arranged to rotate adjacent aHall Effect sensor mounted on a circuit board with appropriateelectronics, thus affording determination of the angular position of themagnet, hence of shaft 312, and thus of the door operated by the driveoutput of operator unit 50. By appropriate selection of componentry, theentire travel of the door can be embraced within a single rotation ofthe encoder magnet, thus providing an absolute position encoder. Such anencoder is known per se from applicant’s Australian Patent No.2008341003, but not for mounting to the clutch housing of a roller dooroperator unit, to be driven directly from the output drive. In priorroller door operators of this sort, the position encoder assembly ismounted in another part of the operator unit, driven by a separatepinion which is itself driven by rotation of the operator’s output drivedrum.

In the device illustrated, the position encoder assembly 1320 uses a 12bit digital encoder, allowing for 4096 discrete positions. This enablesa resolution of approximately 0.5 mm over a 2 m door travel(corresponding to around 5 arc minutes of rotation of the magnet,assuming the door travel is embraced within almost 360° of rotation).

In accordance with the design, clutch assembly 1300 is very slimline inprofile, while comprising in a single unit all the elements (includingthe position encoder) of the drive assembly, the drive assemblytransferring power from motor 210 to the output drive drum. Hence, andin contrast to prior devices, this compact design allows for theintegration of the position encoder assembly to the clutch assemblywhile still maintaining the slimline profile of door operator unit 50.

Thus, it is apparent to a person skilled in the art that the clutchassembly 1300 provides for engaging and disengaging the drive train of adoor operator unit 50. A user can pull the lever arm 1002 once todisengage the clutch assembly 1300, allowing the door 20 to be openedand closed manually. When disengaged, the electric motor 210 cannotdrive the door 20. The user can pull the lever arm 1002 again in thesame manner to engage the clutch assembly 1300 such that the door 20 canonly be driven by the electric motor 210. The door 20 cannot be openedmanually when the clutch assembly is engaged.

Whilst the described embodiment of the clutch assembly 1300 illustratesa configuration, whereby rotation of clutch lever 402 by 90° causesengagement and disengagement of the clutch assembly 1300, other suitableembodiments with any suitable number of components may be provided sothat any suitable rotational distance is traversed to provide theengagement and disengagement mechanism. For example, an alternateembodiment may provide two base mating walls 613 angularly equispaced180°, two clutch cam mating walls 806, 808 angularly equispaced 180°,and one or two clutch lever mating walls 1104. This alternate embodimentmay require rotation of the clutch lever 402 by 180° in order tosuccessfully actuate the clutch assembly 1300. Similarly, more of thesecomponents can be provided, resulting in the clutch lever being rotatedover a lesser angular extent to successfully actuate clutch assembly.

A person skilled in the art will appreciate that the various componentsdescribed can be made from any suitable plastics or metals that satisfythe load and friction requirements of the clutch assembly. In the deviceillustrated, the primary components of clutch assembly 1300 arefabricated from the following materials:

-   Clutch disc 400 - powder steel SMF5040-   Clutch lever 402 - DURACON™ GD-25 POM resin, 25%GF-   Clutch base 600 - DELRIN™ 500 resin-   Clutch cam 700 - HYLON™ 612PA resin-   Clutch cap 1302 - DELRIN™ 500 resin

It will be understood that the invention disclosed and defined in thisspecification extends to all alternative combinations of two or more ofthe individual features mentioned or evident from the text or drawings.All of these different combinations constitute various alternativeaspects of the invention.

1. A clutch assembly for a roller door operator, the clutch assemblyproviding selective engagement between a motor and a door drive via aclutch assembly output drive shaft, the clutch assembly having a clutchbase, a clutch cover and a clutch mechanism including one or more cam orratchet elements arranged to rotate around the axis of said clutchassembly output drive shaft and configured to provide alternateengagement and disengagement between the motor and the clutch assemblyoutput drive shaft with successive actuation and release actions of aclutch lever between a first position and a second position, the clutchassembly including a position encoder unit mountable to said clutchcover, the position encoder unit having an input shaft arranged to bedriven directly by said clutch assembly output drive shaft.
 2. Theclutch assembly of claim 1, wherein said position encoder unit includesan absolute position encoder arranged to sense the rotational positionof a magnetic element driven by rotation of the position encoder inputshaft, configured such that 360° of rotation of the magnetic elementcorresponds to more than the full travel of a door driven by the rollerdoor operator.
 3. The clutch assembly of claim 2, wherein said absoluteposition encoder includes a Hall effect sensor.
 4. The clutch assemblyof claim 2, wherein the position encoder unit includes a worm gear driveconnecting the position encoder input shaft and the magnetic element. 5.The clutch assembly of claim 1, wherein the position encoder unit ismountable to the clutch cover such that the input shaft of the positionencoder is concentric with the output drive shaft of the clutchassembly, input shaft of the position encoder and the output drive shaftof the clutch assembly having complementary shapings for rotationaldrive connection therebetween.
 6. The clutch assembly of claim 5,wherein the output drive shaft of the clutch assembly includes a slotfor engagement by the position encoder shaft.
 7. A door operatorincluding the clutch assembly of claim 1.